Curable compositions having a crosslinkable silyl group-containing vinyl polymer are used as sealing materials for use in buildings for filling spaces between interior or exterior members of buildings or for sealing joints to prevent the invasion of wind and rain, or as adhesives for adhering various adherends. Sealing materials comprising the so-called modified silicone species whose main chain structure is a polyoxyalkylene polymer and which have one or more crosslinkable silyl groups are in wide use because of their good workability and good flexibility in a wide temperature range. In some instances, however, they are not sufficient in weather resistance to meet the recent prolonged working time requirement imposed on buildings, predominately for glazing applications.
In recent years, transparent adherends (photocatalyst-coated transparent substrates) coated with a composition having a photocatalytic activity (titanium oxide) have come into use as exterior materials from the maintenance-free viewpoint. Concerning this use, it has been shown that when modified silicone sealing materials or acrylic-modified silicone sealing materials superresistant to weathering are used, the weather resistant adhesion is unsatisfactory and that when crosslinkable silyl group-containing vinyl copolymer-based curing compositions are used, the surface weather resistance and weather-resistant adhesion properties are improved (cf. e.g. Japanese Patent Application 2003-344180). In the case of photocatalyst-coated transparent materials, however, the activity varies depending on the quantity of the photocatalyst applied to the surface and it is becoming more and more evident that when sealing materials comprising crosslinkable silyl group-containing vinyl copolymer-based curable compositions are applied to highly active photocatalyst-coated transparent materials, the weather-resistant adhesion properties are unsatisfactory in certain instances.
Although it has been shown that the addition of an antioxidant to a vinyl polymer-containing curable composition results in an improvement in thermal stability of the cured products derived from the curable composition (e.g. Japanese Kokai Publication 2003-113324), it has not yet been revealed that such a composition can have such a high level of weather resistant adhesion to photocatalyst-coated adherends as described hereinbelow.